This application is based on Japanese Patent applications Nos. 2000-25892 and 2000-363635 filed in Japan, the contents of which are hereby incorporated by reference.
This invention relates generally to an image forming apparatus such as a digital copier apparatus, printer and the like, and to a digital image photographing apparatus such as a digital camera, and further relates to a color image processing apparatus for correcting colors of image data in consideration of visual characteristics of human beings.
There have conventionally been provided with various correcting methods for reproducing input color images with high fidelity in the above-mentioned image processing apparatus. For example, Japanese patent application publication No. 9-270932 discloses a method of correcting color image data by setting masking coefficients for image reproduction in response to colors of recording media (such as paper) to be used, thereby reproducing a color image with high fidelity even if paper including various colors is used. Further, in order to solve a problem that, even if color printed matter and a color monitor image have an equal color in a color space under certain ambient light, both of appearances of these images change according to changes in the ambient light, Japanese patent application publication No. 9-102882 discloses a method of detecting information about the ambient light and converting colors to be reproduced according to the ambient light.
However, the above conventional arts have not disclosed a correcting method in consideration of visual characteristics of human beings. For example, even if color image data is captured by a color scanner or a camera with high accuracy, and reproduced with high fidelity in response to a paper color or ambient light, it has been impossible to correct the difference in an appearance of color due to visual characteristics of human beings. That is, the conventional arts could not have coped with a problem that the appearance of the foreground in an image changes in response to the background. The phenomenon of changes in the appearance of the color is generally called as a contrast phenomenon wherein, as to hue, the hue of the foreground appears to wear complementary color of the background color, wherein as to brightness value (hereinafter simply referred to as value), the foreground appears to be dark in a light background color, and wherein, as to chroma, the foreground appears to be darkish in the vivid background color. Due to this phenomenon of changes in the appearances of the color, for example, as shown in FIGS. 13(a) and 13(b) in which a man (foreground) appears in the vivid blue of the sea, or green of the grass (background), skin of the man appears to be yellowish in the blue of the sea, and appears to be reddish in the green of the grass.
This invention is made to solve the above-mentioned problems. One object of the present invention is to provide a color image processing apparatus which is capable of correcting changes in colors (contrast phenomenon) of a foreground image caused by a background image due to visual characteristics of human beings, thereby visually reproducing the colors with high fidelity.
In order to achieve the above-mentioned object, according to one aspect of the present invention, a color image processing apparatus which carries out processing for correcting input color image data, comprises: an extracting device for extracting foreground image data and background image data from the input color image data; a detecting device for detecting one or more among hue, value and chroma of the background image data extracted by the extracting device; and a correcting device for correcting one or more among hue, value and chroma of the foreground image data based on one or more among the hue, value and chroma detected by the detecting device.
According to another aspect of the present invention, in the color image processing apparatus, the correcting device corrects one or more among the hue, value and chroma of the foreground color in a direction of color difference of the background color.
According to a further aspect of the present invention in the image processing apparatus, the correcting device carries out the correction when an area composed of the foreground color and background color exceeds a predetermined extent, and does not carry out the correction when the area is smaller than or equal to the predetermined extent.
According to a further aspect of the present invention in the image processing apparatus, the correcting device corrects a color contrast phenomenon that occurs visually.
According to a further aspect of the present invention in the image processing apparatus, the correcting device corrects the one or more among the hue, value and chroma of the foreground color in a reverse to a direction from an actual color difference to a visual color difference by a difference between the actual color difference and the visual color difference.
According to a further aspect of the present invention in the image processing apparatus, the extracting device includes a generator of a histogram about the one or more among the hue, value and chroma of a subject image, wherein, based on the histogram created by the histogram generator, each of frequency histograms about the one or more among the hue, value and chroma is created in X and Y directions, wherein, based on the frequency histograms, addresses about the one or more among the hue, value and chroma distributed in X and Y directions are obtained, and the maximum and minimum addresses are obtained, and wherein, if the maximum and minimum addresses are the same hue (value or chroma), the image having said hue is decided to be a background image, whereas if there is any hue (value or chroma) included in the maximum and minimum addresses, the image having said hue (value or chroma) is decided to be a foreground image.